keisoku

ISO Week Number from Date

Enter any date to find which week of the year it falls in, using the ISO 8601 week number. The weekday, day of the year, and ISO year are shown at the same time.

Input

YYYY/MM/DD

Result

Enter a date.

How it works

  • Enter a date and the tool shows its ISO 8601 week number prominently. Today's date is filled in by default and you can change it freely.
  • Under ISO 8601, weeks begin on Monday and week 1 is the week containing the year's first Thursday. This is the convention used by the international standard and by many business systems and calendars.
  • Along with the week number, the tool shows the weekday (ISO weekday numbers run Monday=1 to Sunday=7), the day of the year counted from January 1, and the calendar year.
  • A few days in late December or early January can be assigned to the adjacent year's weeks. In that case the tool shows an "ISO year" that differs from the calendar year and flags it with a note.
  • Depending on the year, an ISO year has either 52 or 53 weeks. The results panel also shows the total number of weeks in that ISO year.
  • You can share the result directly to X. Use it to check week numbers for project management and weekly reports.